Methods for converting linear polyesters to macrocyclic oligoester compositions and macrocyclic oligoesters

ABSTRACT

Macrocyclic oligoesters and compositions comprising macrocyclic oligoesters are prepared from intermediate molecular weight polyesters. In one embodiment, a diol is contacted with a dicarboxylic acid or a dicarboxylate in the presence of a catalyst to produce a composition comprising a hydroxyalkyl-terminated polyester oligomer. The hydroxyalkyl-terminated polyester oligomer is heated to produce a composition comprising an intermediate molecular weight polyester which preferably has a molecular weight between about 20,000 Daltons and about 70,000 Daltons. The intermediate molecular weight polyester is heated and a solvent is added prior to or during the heating process to produce a composition comprising a macrocyclic oligoester. An optional step is to separate the macrocyclic oligoester from the composition comprising the macrocyclic oligoester.

[0001] This application claims priority to provisional patentapplication U.S. Ser. No. 60/229,894 filed on Sep. 1, 2000, the entirecontents of which are incorporated by reference herein.

TECHNICAL FIELD

[0002] This invention generally relates to macrocyclic polyesters. Moreparticularly, the invention relates to a method for preparingmacrocyclic oligoester compositions from intermediate molecular weightpolyesters.

BACKGROUND INFORMATION

[0003] Macrocyclic oligoesters, also called macrocyclic polyesteroligomer compositions, can be converted, often under isothermalconditions, to linear polyesters of high crystallinity and solventresistance.

[0004] One method for preparing macrocyclic oligoesters is accomplishedby the reaction of diols, such as ethylene glycol or 1,4-butanediol,with dicarboxylic acid chlorides, such as terephthaloyl chloride orisophthaloyl chloride, under specifically defined conditions. Othermethods of preparing macrocyclic polyester oligomer compositions includethe reaction of a dicarboxylic acid chloride, such as terephthaloylchloride, with a bis(hydroxyalkyl)dicarboxylate, such asbis(4-hydroxybutyl)terephthalate.

[0005] Another macrocyclic oligoester preparation method is catalyticdepolymerization of linear polyesters such as poly(1,4-butyleneterephthalate) (“PBT”) and poly(ethylene terephthalate) (“PET”).Catalytic depolymerization macrocyclic oligoester preparation methodsrequire that linear polyesters be purchased or manufactured prior tomacrocyclic oligoester production. Producing macrocyclic oligoestersfrom high molecular weight linear polyesters necessitates handling of ahigh molecular weight material. The high molecular weight linearpolyester material typically has a high viscosity, which requires costlyequipment. In some instances it also requires many expensive finishingsteps.

[0006] For example, prior art methods employ melt reactors that arecapable of generating surface area in high viscosity high molecularweight material. Where poly(butylene terephtalate) is reacted with1,4-butanediol, it is necessary to generate surface area to enable thediol to diffuse to the surface so that the reaction may proceed to buildthe molecular weight of the polymer. When high viscosity high molecularweight materials are prepared, diffusion of the diol from the polymermatrix is rate limiting and generating surface area by employing a meltreactor increases the reaction rate of the process of building themolecular weight of the polymer. Such melt reactors are highlyengineered, energy intensive, and are run under relatively high vacuumconditions (e.g., 0.5 Torr) that are necessary to handle the highviscosity material.

[0007] Further, U.S. Pat. No. 4,590,259 to Kosky et al. describes amethod for preparing poly(alkylene terephthalates) of blow molding gradein which a final step is conducted under conditions necessitated by thehigh melt viscosity of high molecular weight polyesters. A prepolymerpreparation step is described in which, for example, a poly(butyleneterephtalate) undergoes reaction with 1,4-butanediol. The resultingprepolymer undergoes reaction further with the diol in the presence ofan inert gas to reduce the number of acid end groups, for examplecarboxylic acid end groups, to a desired level. Thereafter, solid statepolymerization is conducted whereby the molecular weight of the polymeris increased under high vacuum conditions.

SUMMARY OF THE INVENTION

[0008] The invention generally relates to methods for depolymerizinglinear polyesters to macrocyclic oligomer compositions. In one aspect ofthe invention, an intermediate molecular weight polyester is employed toprepare a composition comprising a macrocyclic oligoester. In oneembodiment, a diol is contacted with a dicarboxylic acid ordicarboxylate in the presence of a catalyst to produce a compositioncomprising a hydroxyalkyl-terminated polyester oligomer. Thereafter, thehydroxyalkyl-terminated polyester oligomer is heated to produce acomposition comprising an intermediate molecular weight polyester whichpreferably has a molecular weight between about 20,000 Daltons and about70,000 Daltons. The intermediate molecular weight polyester is heatedand a solvent is added prior to or during the heating process to producea composition comprising a macrocyclic oligoester. The compositioncomprising macrocyclic oligoester includes, for example, a mixture ofmacrocyclic oligoesters and linear oligoesters. An optional step is toseparate a macrocyclic oligoester from the composition comprising themacrocyclic oligoester.

[0009] Methods of the invention minimize operations and eliminate theneed for costly equipment. Of the steps used to manufacture linearpolyesters, only those steps necessary for ultimate recovery ofmacrocyclic oligomers are employed and integrated with the operationsnecessary to recover a macrocyclic oligomer composition. For example,the use of costly melt reactors is unnecessary. Later steps in prior artpolyester preparation, in particular steps necessary to produce a highmolecular weight product, are eliminated thereby providing a productadequate for conversion to macrocyclic oligomers without significantloss in yield.

[0010] Methods of the invention also permit the use of equipment thattransports low viscosity materials, whereby these methods are lessexpensive than prior art alternatives. According to the invention, lowviscosity intermediate molecular weight polyesters are employed to makemacrocyclic oligoesters. However, compared to the above-describedmethods employing high molecular weight polymers, methods of the presentinvention employing intermediate molecular weight polyesters have anincreased number of linear polyesters with uncyclizable end groupsremaining after cyclization. To promote further reaction to formmacrocyclic oligoesters from intermediate molecular weight polyesters,it may be desirable to remove an uncyclizable end group, e.g., ahydroxyalkoxy group, from the linear polyester to create an intermediatemolecular weight polyester capable of forming a macrocyclic oligoester.Removal of an end group results in by-product diol, which may be thestarting material diol, i.e., the first compound.

[0011] In one embodiment, one or more solvents are employed for removalof by-product diol(s) by distillation, as the by-product diol(s) shouldbe removed before cyclization takes place. The distillation may be, forexample, azeotropic distillation, or distills or co-distills of theby-product diols may distill off at a temperature below the boilingpoint of the solvent. Thus, energy- and equipment-intensive methods, forexample, melt reaction, necessitated by the high melt viscosity of theproduct are replaced by a simple distillation. In addition, the use ofsolvent reduces the viscosity of the macrocyclic polyester product,which enables the process to employ less costly equipment that iscapable of transporting a low viscosity material.

[0012] Thereafter, the removed end groups, which typically result inby-product diols, may be transported and purged as waste from theprocess. Alternatively, a recycling step may be employed to reuse theby-product diol as a reactant in the process. Likewise, the volumedemand on an existing recycling step may increase in order to transportthe by-product diol created during the process. Despite the addition ofsuch a recycling step or the additional volume demand on an existingrecycling step, methods of making macrocyclic oligoesters from lowviscosity intermediate molecular weight polyesters can be morecost-effective than prior methods. The cost benefit is due in part tothe ability to employ simple distillation in place of expensivefinishing steps. Also, transporting low viscosity polyesters is lesscostly then transporting high viscosity material. Macrocyclic oligoesterproduction methods according to the invention can be conductedcontinuously, semi-continuously, according to a batch methodology, or acombination thereof.

[0013] In another aspect, an embodiment of a method for preparing amacrocyclic oligoester composition includes providing an intermediatemolecular weight polyester, a solvent, and a catalyst. The catalyst maycomprise, for example, a tin compound or a titanate compound. Theintermediate molecular weight polyester, solvent, and a catalyst areheated to produce a composition comprising a macrocyclic oligoester. Themethod may further include separating the macrocyclic oligoester fromthe composition comprising the macrocyclic oligoester.

[0014] The foregoing, and other features and advantages of theinvention, as well as the invention itself, will be more fullyunderstood from the description, drawings, and claims which follow.

BRIEF DESCRIPTION OF FIGURES

[0015]FIG. 1 is a schematic flow diagram of an embodiment of a method ofthe invention for making a macrocyclic oligoester.

[0016]FIG. 2 is a schematic flow diagram of another embodiment of amethod of the invention for making a macrocyclic oligoester.

DESCRIPTION

[0017] In one aspect, a method of the invention for preparingmacrocyclic oligoesters generally includes contacting a first compoundhaving a structural formula:

HO—R—OH   (I)

[0018] where R is an alkylene, a cycloalkylene, or a mono- orpolyoxyalkylene group, with a second compound having a structuralformula:

BOOC-A-COOB   (II)

[0019] where A is a divalent aromatic group or an alicyclic group, and Bis hydrogen or an alkyl group. The compounds of formulas (I) and (II)are contacted in the presence of a first catalyst to produce acomposition comprising a hydroxyalkyl-terminated polyester oligomer.Heating the composition comprising the hydroxyalkyl-terminated polyesteroligomer at a reduced pressure produces a composition comprising anintermediate molecular weight polyester. Heating the compositioncomprising the intermediate molecular weight polyester in the presenceof a solvent produces a composition comprising a macrocyclic oligoester.Optionally, the macrocyclic oligoester is separated from the compositioncomprising the macrocyclic oligoester.

[0020] Referring to FIG. 1, in which a flow diagram depicts anembodiment of a method of the invention, an intermediate molecularweight polyester is employed to prepare a composition comprising amacrocyclic oligoester. A first compound 10 is contacted with a secondcompound 14 in the presence of a first catalyst 18 (STEP 80) to producea composition comprising a hydroxyalkyl-terminated polyester oligomer90.

[0021] The first compound 10 has the structural formula HO—R—OH. Thesubstituent “R” may be, for example, an alkylene, a cycloalkylene, or amono- or polyoxyalkylene group. The mono- or polyoxyalkylene group mayinclude between about 2 and about 8 carbon atoms. In one embodiment, thepolyoxyalkylene group includes a polyoxyalkylene radical. In someembodiments, the alkylene is ethylene —(CH₂CH₂)—, tetramethylene—((CH₂)₄)—, or a mixture thereof. 1,2-Ethanediol (R=ethylene) may beemployed when producing the homopolymer, poly(ethylene terephthalate)(“PET”). Alternatively, to produce poly(butylene terphthalate) (“PBT),1,4 butanediol (R=tetramethylene) may be employed. A mixture of thesecompounds may be used to produce a copolymer, for example, the copolymerpoly(butylene terphthalate)/poly(ethylene terephthalate) (“PBT/PET”).

[0022] The first compound 10 may be an aliphatic diol. In anotherembodiment, a mixture of diols may include only alkylene glycols suchas, for example, ethylene glycol and 1,4-butanediol, or may additionallyinclude ether diols such as diethylene glycol, the product of which isemployed to produce a macrocyclic copolyester oligomer.

[0023] In one embodiment, the second compound 14 has the structuralformula BOOC-A-COOB. The substituent “A” may be, for example, a divalentaromatic group or an alicyclic group. The alicyclic group may be analicyclic radical, for example, a meta-linked or a para-linked monocylicradical. In one embodiment, the para-linked aromatic group is apara-linked benzene group. In another embodiment, the substituent “A” isa meta- or para-phenylene or a mixture thereof. The substitutent “B” maybe, for example, hydrogen or an alkyl group. The alkyl group preferablyhas from 1 to 6 carbon atoms. Commonly used alkyl groups include methyland ethyl.

[0024] In an exemplary embodiment, the second compound 14 includes oneor more aromatic dicarboxylic acids or alkyl esters thereof. Thedicarboxylic acid or acids may be employed in their free acid form or,preferably, in the form of an alkyl ester, most often in the form of adiester, for example, a di-(C₁₋₄ alkyl) ester such as dimethylterephthalate. Thus, the preferred polyesters are poly(butyleneterephthalate) (“PBT”), poly(ethylene terephthalate) (“PET”), thecorresponding isophthalates, and copolyesters thereof, i.e., PBT/PET.

[0025] When contacting the first compound 10 and the second compound 14(STEP 80), any conditions may be employed so long as they promote thereaction. Such conditions may include, for example, providing the firstcompound 10 and the second compound 14 in a molar ratio between about1.05:1 and about 1.5:1. An amount of catalyst 18 in the range of fromabout 0.1 mole percent to about 5 mole percent based on the firstcompound may be provided to promote the reaction conducted in STEP 80.In some embodiments, the amount of catalyst ranges between about 1 molepercent to about 5 mole percent based on the first compound.

[0026] When an ester such as dimethyl terephthalate is employed, it ispreferred to employ a temperature at which the displaced alkanol will beremoved by distillation, thus driving the reaction toward formation ofthe desired hydroxyalkyl-terminated polyester oligomer composition 90.In one embodiment, the first compound 10 contacts the second compound 14and the temperature is held between about 140° C. and about 200° C. Inanother embodiment, the first compound 10 contacts the second compound14 and the temperature is held between about 160° C. and about 180° C.In yet another embodiment, the first compound 10 contacts the secondcompound 14 and the temperature is held between about 180° C. and about200° C.

[0027] The catalyst(s) employed in the practice of the invention areadapted to polyester preparation. More specifically, catalysts employedin the invention are those that are capable of catalyzing atransesterification polymerization of a macrocyclic oligoester with adihydroxyl-functionalized polymer. Numerous such catalysts are known inthe art. The catalysts may comprise a tin compound or a titanatecompound. As with state-of-the-art processes for polymerizingmacrocyclic oligoesters, organotin and organotitanate compounds are thepreferred catalysts, although other catalysts may be used. One or morecatalysts may be used together or sequentially.

[0028] Illustrative examples of classes of tin compounds that may beused in the invention include monoalkyltin(IV) hydroxide oxides,monoalkyltin(IV) chloride dihydroxides, dialkyltin(IV) oxides,bistrialkyltin(IV) oxides, monoalkyltin(IV) trisalkoxides,dialkyltin(IV) dialkoxides, trialkyltin(IV) alkoxides, tin compoundshaving the formula (III):

[0029] and tin compounds having the formula (IV):

[0030] wherein R₂ is a C₁₋₄ primary alkyl group, and R₃ is C₁₋₁₀ alkylgroup.

[0031] Specific examples of organotin compounds that may be used in thisinvention include dibutyltin dioxide,1,1,6,6-tetra-n-butyl-1,6-distanna-2,5,7,10-tetraoxacyclodecane,n-butyltin(IV) chloride dihydroxide, di-n-butyltin(IV) oxide, dibutyltindioxide, di-n-octyltin oxide, n-butyltin tri-n-butoxide,di-n-butyltin(IV) di-n-butoxide,2,2-di-n-butyl-2-stanna-1,3-dioxacycloheptane, and tributyltin ethoxide.See, e.g., U.S. Pat. No. 5,348,985 to Pearce et al. In addition, tincatalysts, and other catalysts including titanate compounds described incommonly owned U.S. Ser. No. 09/754,943, may be used in thepolymerization reaction.

[0032] Titanate compounds may be used in the invention and illustrativeexamples of titanate compounds include tetraalkyl titanates (e.g.,tetra(2-ethylhexyl) titanate, tetraisopropyl titanate, and tetrabutyltitanate), isopropyl titanate, titanate ester, titanate tetraalkoxide.Other illustrative examples include (a) titanate compounds having theformula (V):

[0033] wherein each R₄ is independently an alkyl group, or the two R₄groups taken together form a divalent aliphatic hydrocarbon group; R₅ isa C₂₋₁₀ divalent or trivalent aliphatic hydrocarbon group; R₆ is amethylene or ethylene group; and n is 0 or 1, (b) titanate estercompounds having at least one moiety of the formula (VI):

[0034] wherein each R₇ is independently a C₂₋₃ alkylene group; Z is O orN; R₈ is a C₁₋₆ alkyl group or unsubstituted or substituted phenylgroup; provided when Z is O, m=n=0, and when Z is N, m=0 or 1 and m+n=1,and (c) titanate ester compounds having at least one moiety of theformula (VII):

[0035] wherein each R₉ is independently a C₂₋₆ alkylene group; and q is0 or 1.

[0036] Referring again to FIG. 1, as described previously, the firstcompound 10 and the second compound 14 are contacted (STEP 80) in thepresence of an above-described catalyst 18 to produce a compoundcomprising a hydroxyalkyl-terminated polyester oligomer 90. Thecondensation reaction which takes place in STEP 80 can be consideredcomplete when no remaining alkanol, usually methanol, is found in thedistillate. It is usually found that some diol is removed with thealkanol, but diol removal is primarily the function of the later heatingsteps, (e.g., STEP 100 and STEP 120) described below.

[0037] The hydroxyalkyl-terminated polyester oligomer 90 is heated in afirst heating step (STEP 100) to produce a composition comprising anintermediate molecular weight polyester 110. In one embodiment, thehydroxyalkyl-terminated polyester oligomer 90 composition is heatedunder reduced pressure (i.e., pressure less than atmospheric pressure)whereupon further condensation takes place with removal of diol bydistillation, producing a composition comprising an intermediatemolecular weight polyester 110. Temperatures in the range of about180-275° C. and pressures in the range of about 5-625 torr are typicallyemployed in this heating step (STEP 100).

[0038] In one embodiment, the one or more solvents are employed forremoval of by-product diol by distillation, where the by-product diolshould be removed before cyclization takes place. The distillation maybe, for example, azeotropic distillation. Alternatively, distills orco-distills of the by-product diol may distill off at a temperaturebelow the boiling point of the solvent. Preferably, the boiling point ofthe selected solvent is higher then the boiling point of the diol thatis being removed. Thus, energy- and equipment-intensive methods such as,for example, melt reaction, necessitated by the high melt viscosity ofthe product are replaced by a simple distillation. The added solventreduces the viscosity of the macrocyclic polyester product, whichenables less costly equipment, which is capable of transporting lowviscosity product to be employed in this process.

[0039] In some embodiments, during the first heating step (STEP 100) asecond catalyst is added to the composition comprisinghydroxyalkyl-terminated polyester oligomer 90. One or more of theabove-described catalysts may be employed. In one embodiment, the secondcatalyst that is added in the heating step (STEP 100) is identical tothe first catalyst 18 that was introduced in the prior step (STEP 80).The second catalyst may be added, for example, to speed the rate ofreaction or to replenish inactivated catalyst.

[0040] In another embodiment, the first heating step (STEP 100) isaccomplished in multiple stages. For example, first and second stagesmay be employed. In an exemplary embodiment, the first stage includesheating at a temperature between about 175° C. and about 200° C. and areduced pressure of between about 550 torr and about 625 torr.Thereafter, the second stage includes heating at an increasedtemperature between about 225° C. and about 275° C. and a decreasedreduced pressure of between about 5 torr and about 15 torr.

[0041] In yet another embodiment, the heating step (STEP 100) isconducted until polymerization is about 95-98% complete, e.g., asestimated by the proportion of diol (i.e., the first compound 10)removed by distillation. In one embodiment, aliphatic diol is removedvia distillation. In the first heating step (STEP 100), it is notnecessary to remove all traces of diol, as any remaining diol isefficiently removed in the second heating step (STEP 120) as describedhereinafter. The product of the first heating step (STEP 100) is acomposition comprising intermediate molecular weight polyester 110. Theintermediate molecular weight polyester 110 may be predominantly linearand in some embodiments it may contain hydroxyalkyl end groups in minorproportion.

[0042] In one embodiment, the molecular weight of the intermediatemolecular weight polyester is between about 20,000 Daltons and about70,000 Daltons. In another embodiment, the molecular weight of theintermediate molecular weight polyester is between about 30,000 Daltonsand about 60,000 Daltons. In yet another embodiment, the molecularweight of the intermediate molecular weight polyester is between about40,000 Daltons and about 50,000 Daltons.

[0043] The intermediate molecular weight polyester 110 is heated and asolvent 114 is added (STEP 120) to form a composition comprising amacrocyclic oligoester 130. In one embodiment, the second heating step(STEP 120) is employed to remove remaining hydroxyalkyl end groupscreating one or more appropriate reactive sites to cause cyclization toform macrocyclic oligomers. The method employs a solvent 114 for threepurposes: to lower the viscosity of the mixture, to aid in the removalof by-product diol by distiallation, and to provide high dilutionconditions which promote cyclization. The hydroxyalkyl end groups thatwere converted to by-product diol may be recycled within the process byadding the by-product diol to the first compound 10 in STEP 80.Alternatively, the by-product diol may be removed as waste. Theintermediate molecular weight polyester 110 may be heated to the refluxtemperature of the added solvent 114, for example, a temperature betweenabout 150° C. and about 200° C.

[0044] In some embodiments, a diol, i.e., a by-product diol, is producedin the second heating step (STEP 120). The solvent 114 that is employedis capable of forming a mixture with the by-product diol, and removesthe last traces of the by-product diol by distillation to afford amacrocyclic oligoester composition 130.

[0045] In certain embodiments, it may be desirable to add the solvent intwo stages. In a first stage, the solvent is added to assist in theremoval of by-product diol that results from the removal of uncyclizedend groups from linear polyesters. In the first stage, the amount ofintermediate molecular weight polyester in the mixture may increase.Also, the molecular weight of the intermediate molecular weightpolyester may increase. In a second stage more solvent is added toprovide dilute conditions that promote cyclization and may increase theyield of macrocyclic oligoesters.

[0046] Solvents that may be used may be capable of forming an azeotropicmixture with the by-product diol to be removed, for example, with1,4-butanediol in the case of PBT processing. Alternative solvents maybe employed so that the distills or co-distills may distill off at atemperature below the temperature of the solvent.

[0047] In one embodiment, the solvent 114 comprises a halogenatedaromatic hydrocarbon, for example, ortho-dichlorobenzene.Ortho-dichlorobenzene is particularly useful for treatment of PBT. Inanother embodiment, the solvent 114 is added in an amount to produce amixture containing from about 5% to about 25% solids by weight, that is,about 5-25% of linear and cyclic polyesters. The mixture may be asolution. In yet another embodiment, the solvent 114 is added to dilutethe composition comprising intermediate molecular weight polyester 110to about one tenth normal (0.1 N) concentration. The added solvent 114provides dilute conditions that promote cyclization. By cyclizingintermediate molecular weight oligomers rather then high molecularweight oligomers, the method avoids reaction kinetics that require largesized reactors (i.e., second order kinetics or higher).

[0048] In some embodiments, the cyclization yield is generally dependentupon the dilution of macrocyclic oligoester. More dilute conditionstypically provide a higher yield of cyclics in the compositioncomprising macrocyclic oligoesters 130. Table 1 illustrates therelationship between dilution conditions, i.e., the molar concentrationof macrocyclic oligoesters based on a monomer molecular weight of 220Daltons PBT where a terephthalic acid derivative solvent is employed,and yield (see e.g. Table 1). In Table 1, the percentage yield ofmacrocyclic oligoester was analytically determined using HPLC analysis,assuming a molecular weight of 220 Daltons. Suitable HPLC equipment isavailable from Hewlett Packard (Palo Alto, Calif.). TABLE 1 MolarConcentration Percentage Yield Experiment Number (M) (%) 1 0.049 72 20.06 65.6 3 0.076 66.6 4 0.091 54.1 5 0.125 42.7 6 0.195 27.9

[0049] In some embodiments, a third catalyst is added in the secondheating step (STEP 120 ) to the composition comprising intermediatemolecular weight polyester. The catalyst may be any compoundcatalytically effective for depolymerization of a linear polyester tomacrocyclic oligomer species. Also useful are catalysts effective forpolymerization of macrocyclic oligomers to linear polyesters, since thisreaction is the reverse of the depolymerization reaction and employs thesame catalysts with changes in other conditions such as dilution.Numerous compounds with such activity are known in the art, for example,the titanium and tin compounds described in U.S. Pat. Nos. 5,407,984;5,668,186; 5,389.719; 5,466,744; 5,527,976; 5,648,454; 5,661,214; and5,710,086.

[0050] Among the compounds active as depolymerization catalysts, asnoted in the aforementioned U.S. Pat. No. 5,466,744, are the tetraalkyltitanates employed in contacting step (STEP 80) and the first heatingstep (STEP 100) of the present invention. Thus, it may be possible toconduct the second heating step (STEP 120) without addition of furthercatalyst. It is sometimes advisable to replenish the catalyst, however,since some loss of activity may occur in the prior steps (STEP 80 andSTEP 100). Whether or not catalyst replenishment is necessary can bedetermined by monitoring the rate of the reaction. For example, in someembodiments, catalyst is added in the first step (STEP 80) andadditional catalyst is added in the second heating step (STEP 120), uponreduction of the reaction rate.

[0051] The amount of catalyst, if any, added in the second heating step(STEP 120) may be identical or similar to the quantity of catalystintroduced in the first step (STEP 80). In an exemplary embodiment, thetype of catalyst that is added in the second heating step (STEP 120) isthe same as the type of catalyst that is added in the first step (STEP80). In another embodiment, the type of catalyst added in the secondheating step (STEP 120) is different then the type of catalyst that wasadded in the first step (STEP 80).

[0052] Upon completion of the second heating step (STEP 120), thecomposition comprising a macrocyclic oligoester is formed. In oneembodiment, water is added during the second solvent removal. In anotherembodiment, water is added after the second heating step. The quantityof water that may be added may be the molar equivalent of the totalcatalyst used. For example, where a total of 10 mmol of catalyst havebeen used in the process (STEP 80, STEP 100, and STEP 120) then 10 mmolof water may be added upon completion of STEP 120 to quench the reactionmixture and terminate the reaction.

[0053] In yet another embodiment, an additional step (STEP 140) isconducted to separate macrocyclic oligoesters from the compositioncomprising macrocyclic oligoesters. In some embodiments, the compositioncomprising macrocyclic oligoesters includes macrocyclic oligomers andlinear oligomers. In some embodiments, linear polyester is separatedfrom the composition comprising macrocyclic oligester resulting in amaterial in which the principal constituents are macrocyclic oligoester,normally a mixture of oligoesters of varying degrees of polymerizationwhere those between about 2 and about 7 are present in greatestproportion.

[0054] Separation methods employed in the separating step (STEP 140) toremove the linear polyester may be selected from such operations knownin the art as filtration, filtration at a reduced temperature, andadsorption. For example, the mixture may be cooled and filtered toremove linears. The filtrate may then be subjected to adsorption usingalumina to remove final traces of linears, alternatively, adsorption maybe accomplished using column chromatography with silica to remove finaltraces of linears. After the final traces of linears are removed, themacrocyclic oligoesters may be isolated by precipitation with anon-solvent, typically an aliphatic hydrocarbon, and preferably a C₆₋₁₀hydrocarbon such as heptane.

[0055] In one exemplary embodiment, a method for preparing a macrocyclicoligoester composition includes conducting a reaction between at leastone aliphatic diol and at least one aromatic dicarboxylic acid or alkylester thereof as reactants in the presence of a catalyst, to produce ahydroxyalkyl-terminated polyester oligomer composition (STEP 80). Themethod includes heating the hydroxyalkyl-terminated polyester oligomerunder reduced pressure to distill off aliphatic diol, thereby producinga intermediate molecular weight polyester (STEP 100). The methodincludes heating the intermediate molecular weight polyester in thepresence of a catalyst and a solvent that is capable of forming amixture with the aliphatic diol. The last traces of the aliphatic diolare removed by distillation to afford a composition comprising amacrocyclic oligoester (STEP 120). The method includes removing linearpolyester from the macrocyclic oligomer-enriched polyester composition(STEP 140).

[0056] In one embodiment, the reactants in the reaction (STEP 80) areethylene glycol and/or 1,4-butanediol and dimethyl terephthalate, wherethese reactants yield a PBT/PET co-polymer. In another embodiment,1,4-butanediol is reacted with dimethyl terephthalate to yield a PBThomopolymer. In another embodiment, the catalyst 18 is a titanate ester.In another embodiment, the titanate ester is tetraisopropyl titanate. Inanother embodiment, the temperature of the reaction (STEP 80) is one atwhich displaced methanol is removed by distillation. In anotherembodiment, the temperature of the reaction step (STEP 80) is in therange of about 140-200° C.

[0057] In one embodiment, the solvent employed in the second heatingstep (STEP 120) is a halogenated aromatic hydrocarbon. In anotherembodiment, the solvent is orotho-dichlorobenzene. In one embodiment,the catalyst employed in the reaction (STEP 80) is also active in thesecond heating step (STEP 120). In another embodiment, additionalcatalyst is added in the second heating step (STEP 120). In anotherembodiment, the amount of solvent employed is an amount to produce asolution containing about 5-25% solids by weight. In another embodiment,the method includes a quenching operation following the second heatingstep (STEP 120). In one embodiment, the separation step (STEP 140)includes filtration or adsorption.

[0058] Referring to FIG. 2, in another aspect of the invention, a methodfor preparing a macrocyclic oligoester composition includes providing anintermediate molecular weight polyester, providing a solvent and acatalyst (STEP 210). In some embodiments, a composition comprisingintermediate molecular weight polyester is provided. As described above,in one embodiment, the intermediate molecular weight polyester has amolecular weight between about 20,000 Daltons and about 70,000 Daltons.A solvent 214 and a catalyst 218 are added.

[0059] The intermediate molecular weight polyester, solvent 214, andcatalyst 218 are heated (STEP 220) to produce a composition comprising amacrocyclic oligoester 230. In this step (STEP 220), as described abovein relation to the second heating step of FIG. 1 (STEP 120), the addedsolvent 214 aids in the removal of by-product diol by distiallation,provides high dilution conditions which promote cyclization, and lowerthe viscosity of the mixture.

[0060] In certain embodiments, it may be desirable to add the solvent intwo stages. In a first stage, solvent is added to assist in the removalof by-product diol that results from the removal of uncyclized endgroups from linear polyesters. In the first stage, the amount ofintermediate molecular weight polyester in the mixture may increase.Also, the molecular weight of the intermediate molecular weightpolyester may increase. In a second stage more solvent is added toprovide dilute conditions that promote cyclization and may increase theyield of macrocyclic oligoesters.

[0061] The by-product diol may be recycled within the process bycontacting the by-product diol to the second compound 14 in (STEP 80).Alternatively the by-product diol may be removed as waste. Theby-product diol may be, for example, 1,4-butane diol. The catalyst 218that is employed affects the rate of reaction. The type and quantity ofcatalyst 218 that may be employed may be the type and quantity ofcatalyst 18 that is described above with regard to FIG. 1.

[0062] Similarly, the type and quantity of solvent 214 that may beemployed in this embodiment (STEP 220) is the same as the type andquantity of solvent 114 that is described above in the second heatingstep of FIG. 1 (STEP 120). For example, the solvent 214 may be added inan amount to produce a solution containing from about 5% to about 25%solids by weight. The solvent 214 that may be added may include, forexample, 1,4-butanediol, a halogenated aromatic hydrocarbon, or ahalogenated aromatic hydrocarbon comprising ortho-dichlorobenzene. Theintermediate molecular weight polyester may be heated to a temperaturebetween about 150° C. and about 200° C.

[0063] In one embodiment, the method is complete when the compositioncomprising macrocyclic oligoester 230 is formed, which is uponcompletion of the heating step (STEP 220). In another embodiment, wateris added after the heating step to quench the reaction mixture andterminate the reaction prior to solvent removal. The quantity of waterthat may be added may be the molar equivalent of the total catalystused. For example, where a total of 10 mmol of catalyst have been usedin the process (STEP 210 and STEP 220) then 10 mmol of water may beadded upon completion of (STEP 220) to quench the reaction mixture andterminate the reaction.

[0064] In yet another embodiment, a separation step (STEP 240) may beemployed to separate macrocyclic oligoesters from the compositioncomprising macrocyclic oligoesters 230. In some embodiments, linearpolyester is separated from the composition comprising macrocyclicoligester 230 to leave a material in which the principal constituentsare macrocyclic oligoester, normally a mixture of oligoesters of varyingdegrees of polymerization where those between about 2 and about 7 arepresent in greatest proportion. Separation methods employed in theseparation step to remove the linear polyester may be selected from suchoperations known in the art as filtration, filtration at a reducedtemperature, and adsorption.

[0065] The invention is illustrated further by the followingnon-limiting examples. In the examples, each of the steps of FIG. 1(STEPS 80, 100, 120, and 140) is described in a separate example.Frequently, however, these steps can and will be performed as a singlesequence.

EXAMPLE 1

[0066] As an example of STEP 80, a 3-necked flask fitted with a stirrer,thermometer and vacuum-jacketed Vigreux distillation column, chargedwith 100 g (515 mmol) of dimethyl terephthalate, 72.21 g (802 mmol) of1,4-butanediol and 7.1 g (25 mmol) of isopropyl titanate. Vigreuxdistillation column obtained from Ace Glass, Incorporated (Vineland,N.J.). The resulting mixture was heated over 90 minutes to 175° C., withstirring, as methanol was removed by distillation. At the end of thisperiod, some 1,4-butanediol was also removed. The product was thedesired 4-hydroxybutyl-terminated PBT oligomer composition asanalytically determined by HPLC. The analysis employed a Hewlett PackardHPLC, Model 1110 (Palo Alto, Calif.) equipped with a diode arraydetector set at 254 nM, a Zorbax C-8 reverse phase column maintained at40° C. with a solvent gradient of acetonitrile and water.

EXAMPLE 2

[0067] As an example of STEP 100, the pressure in the flask of Example 1was reduced to 600 torr and distillation was continued at 195° C. for 60minutes. The pressure was reduced further as distillation of1,4-butanediol was continued at 215° C/150 torr for 45 min, 230° C./40torr for 40 min and 240° C./10 torr for 40 min. The flask was cooled to180° C. and returned to atmospheric pressure, yielding a PBT ofintermediate molecular weight of about 20,000 Daltons weighing 113grams. The molecular weight of the intermediate molecular weight PBT isdetermined by gel permeation chromatography (GPC) relative topolystyrene standards using an Hewlett Packard HPLC, Model 1050 (PaloAlto, Calif.). The HPLC is equipped with a fixed wavelength detector setat 254 nM, two linear Phenogel GPC columns where each column measures300 mm×7.8 mm and the Phenogel has a 5 micron particle size andmaintained at a temperature of 40° C. The solvent, chloroform (CHCl₃) ispassed through the GPC columns at a rate of 1.0 mL/min.

EXAMPLE 3

[0068] As an example of STEP 120 or STEP 220, ortho-dichlorobenzene(o-DCB), 1,300 ml, was added to the flask of Example 3 to produce asolution with 10% solids concentration. Heating under reflux was begunand o-DCB was removed by distillation. Samples of the product wereperiodically removed and their average molecular weight were determinedas described above, by GPC relative to polystyrene standards using anHewlett Packard HPLC, Model 1050 (Palo Alto, Calif.), and when themolecular weight value reached 100,000 Daltons, an additional 6.84liters of o-DCB was added and heating under reflux was resumed for 1.5hrs. The reaction was then quenched by the addition of 2 ml of water and70% of the o-DCB was removed with 1,4-butanediol by azeotropicdistillation, yielding a PBT composition enriched in macrocyclicoligomer content as analytically determined according to the abovedescribed methods by HPLC employing a Hewlett Packard HPLC, Model 1110(Palo Alto, Calif.).

EXAMPLE 4

[0069] As an example of STEP 140 or STEP 240, the composition of Example3 was cooled to 70° C. and insoluble linear polyester was removed byfiltration using a Buchner funnel under vacuum conditions. The filtratewas passed through an alumina column to remove additional linearsincluding residual end groups; combined linears could be recycled forconversion to cyclics or conversion by depolymerization to dimethylterephthalate. Suitable alumina is alumina with Brockman Activity GradeI available from Whatman (Clifton, N.J.) that is packed into a standardlaboratory column.

[0070] Further concentration to 50% solids was effected by o-DCBstripping which was determined effected when a quantity of o-DCB wascondensed off of the process. Heptane was introduced in a threefoldvolume amount, resulting in the precipitation of the desired macrocyclicPBT oligomer mixture, which was removed by filtration and dried invacuum. The macrocyclic PBT could be polymerized by contact with astannoxane catalyst at 190° C.

[0071] In the following example, the steps (STEPS 210 and 220) of FIG. 2are described.

EXAMPLE 5

[0072] As an example of STEP 210, 2.15 grams of PBT of intermediatemolecular weight, 42,000 Daltons, is provided. The molecular weight ofthe intermediate molecular weight PBT was determined by gel permeationchromatography (GPC) relative to polystyrene standards according to theabove described methods employing a Hewlett Packard HPLC, Model 1050.143 grams of the solvent o-DCB was added to the 2.15 grams ofintermediate molecular weight PBT. This stirred reaction mixture washeated to reflux, where 15 grams of o-DCB was removed by azeotropicdistillation to complete the drying of the 0.1 Molar mixture of PBT ando-DCB and to form a dry solution. Then 0.49 mmole of organo titanatecatalyst was added to the dry solution.

[0073] In STEP 220, the PBT catalyst and dry solution was heated atreflux for a period of 30 min. to produce a macrocyclic oligoester. Theproduction of macrocyclic oligoester was confirmed when HPLC analysisassuming a molecular weight of 220 Daltons demonstrated that macrocyclicoligoester in the form of an oligomeric cyclic array was present at aconcentration of 9.3 g/L, which is a 48% yield. The analysis employedthe above-described Hewlett Packard HPLC, Model 1110.

[0074] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof Theforegoing embodiments are therefore to be considered in all respectsillustrative rather than limiting on the invention described herein.Scope of the invention is thus indicated by the appended claims ratherthan by the foregoing description, and all changes which come within themeaning and range of equivalency of the claims are intended to beembraced therein.

[0075] Each of the patent documents and scientific publicationsdisclosed hereinabove is incorporated by reference herein.

What is claimed is:
 1. A method for preparing a macrocyclic oligoestercomprising the steps of: (a) contacting a first compound having astructural formula: HO—R—OH   (I) wherein R is an alkylene, acycloalkylene, or a mono- or a polyoxyalkylene group; with a secondcompound having a structural formula: BOOC-A-COOB   (II) wherein A is adivalent aromatic group or an alicyclic group, and B is hydrogen or analkyl group; in the presence of a first catalyst to produce acomposition comprising a hydroxyalkyl-terminated polyester oligomer; (b)heating the composition comprising the hydroxyalkyl-terminated polyesteroligomer at a reduced pressure to produce a composition comprising anintermediate molecular weight polyester; and (c) heating the compositioncomprising the intermediate molecular weight polyester in the presenceof a solvent to produce a composition comprising a macrocyclicoligoester.
 2. The method of claim 1 wherein R is ethylene,tetramethylene, or a mixture thereof.
 3. The method of claim 1 whereinthe mono- or polyoxyalkylene group comprises between 2 and 8 carbonatoms.
 4. The method of claim 1 wherein the alicyclic group is apara-linked aromatic group.
 5. The method of claim 4 wherein thepara-linked aromatic group is a para-linked benzene group.
 6. The methodof claim 1 wherein the first catalyst comprises a tin compound or atitanate compound.
 7. The method of claim 6 wherein the tin compoundcomprises a compound selected from the group consisting of: (a)monoalkyltin(IV) hydroxide oxide, (b) monoalkyltin(IV) chloridedihydroxide, (c) dialkyltin(IV) oxide, (d) bistrialkyltin(WV) oxide, (e)monoalkyltin(IV) trisalkoxide, (f) dialkyltin(IV) dialkoxide, (g)trialkyltin(IV) alkoxide, (h) a tin compound having the formula:

and (i) a tin compound having the formula:

wherein: R₂ is a C₁₋₄ primary alkyl group, and R₃ is C₁₋₁₀ alkyl group.8. The method of claim 6 wherein the titanate compound comprises acompound selected from the group consisting of: (a) tetraisopropyltitanate, (b) isopropyl titanate, (c) tetraalkyl titanate, (d) titanatetetraalkoxide, (e) a titanate compound having the formula:

wherein: each R₄ is independently an alkyl group, or the two R₄ groupstaken together form a divalent aliphatic hydrocarbon group; R₅ is aC₂₋₁₀ divalent or trivalent aliphatic hydrocarbon group; R₆ is amethylene or ethylene group; and n is 0 or 1, (f) a titanate estercompound having at least one moiety of the formula:

wherein: each R₇ is independently a C₂₋₃ alkylene group; Z is O or N; R₈is a C₁₋₆ alkyl group or unsubstituted or substituted phenyl group;provided when Z is O, m=n=0, and when Z is N, m=0 or 1 and m+n=1, and(g) a titanate ester compound having at least one moiety of the formula:

wherein: each R₉ is independently a C₂₋₆ alkylene group; and q is 0or
 1. 9. The method of claim 1 wherein the molar ratio of the firstcompound to the second compound is between about 1.05:1 and about 1.5:1.10. The method of claim 1 wherein the first catalyst is present in anamount from about 1 mole percent to about 5 mole percent of the firstcompound.
 11. The method of claim 1 wherein step (a) further comprisescontacting the first compound and the second compound at a temperaturebetween about 140° C. and about 200° C.
 12. The method of claim 1wherein step (b) further comprises adding a second catalyst to thecomposition comprising the hydroxyalkyl-terminated polyester oligomer.13. The method of claim 12 wherein the first catalyst and the secondcatalyst are identical.
 14. The method of claim 1 wherein step (b)comprises heating at reduced temperature between about 180° C. and about275° C.
 15. The method of claim 1 wherein step (b) comprises heating ata reduced pressure between about 5 torr and about 625 torr.
 16. Themethod of claim 1 wherein the step (b) comprises a first stage and asecond stage.
 17. The method of claim 16 wherein the first stagecomprises heating at a temperature between about 175° C. and about 200°C. and a reduced pressure of between about 550 torr and about 625 torr,and the second stage comprises heating at a temperature between about225° C. and about 275° C. and a reduced pressure of between about 5 torrand about 15 torr.
 18. The method of claim 1 wherein the product of step(b) has a percentage yield between about 95% and about 98%.
 19. Themethod of claim 1 wherein the molecular weight of the intermediatemolecular weight polyester is between about 20,000 Daltons and about70,000 Daltons.
 20. The method of claim 1 wherein the molecular weightof the intermediate molecular weight polyester is between about 30,000Daltons and about 60,000 Daltons.
 21. The method of claim 1 wherein themolecular weight of the intermediate molecular weight polyester isbetween about 40,000 Daltons and about 50,000 Daltons.
 22. The method ofclaim 1 wherein step (c) comprises heating at a temperature betweenabout 150° C. and about 200° C.
 23. The method of claim 1 wherein step(c) comprises adding a third catalyst to the composition comprising theintermediate molecular weight polyester.
 24. The method of claim 23wherein the first catalyst and the third catalyst are identical.
 25. Themethod of claim 1 wherein a diol is produced in step (c), and whereinthe solvent is capable of forming an azeotrope with the diol.
 26. Themethod of claim 25 wherein the solvent comprises a halogenated aromatichydrocarbon.
 27. The method of claim 26 wherein the halogenated aromatichydrocarbon is ortho-dichlorobenzene.
 28. The method of claim 1 whereinstep (c) comprises adding the solvent in an amount to produce a mixturecontaining from about 5% to about 25% solids by weight.
 29. The methodof claim 1 wherein the method further comprises adding water to thecomposition comprising the macrocyclic oligoester.
 30. The method ofclaim 1 further comprising the step of: (d) separating the macrocyclicoligoester from the composition comprising the macrocyclic oligoester.31. The method of claim 30 wherein step (d) comprises separating themacrocyclic oligoester by filtering.
 32. The method of claim 31 whereinstep (d) comprises separating the macrocyclic oligoester by filtering ata reduced temperature.
 33. The method of claim 30 wherein step (d)comprises separating the macrocyclic oligoester by adsorption.
 34. Amethod for preparing a macrocyclic oligoester comprising the steps of:(a) providing a composition comprising an intermediate molecular weightpolyester; and (b) heating the composition comprising the intermediatemolecular weight polyester in the presence of a catalyst and a solventto produce a composition comprising the macrocyclic oligoester.
 35. Themethod of claim 34 further comprising the step of: (c) separating themacrocyclic oligoester from the composition comprising the macrocyclicoligoester.
 36. The method of claim 34 wherein the molecular weight ofthe intermediate molecular weight polyester is between about 20,000Daltons and about 70,000 Daltons.
 37. The method of claim 34 whereinstep (b) comprises heating at a temperature between about 150° C. andabout 200° C.
 38. The method of claim 34 wherein a diol is produced instep (b), and wherein the solvent is capable of forming an azeotropewith the diol.
 39. The method of claim 34 wherein the solvent comprisesa halogenated aromatic hydrocarbon.
 40. The method of claim 34 whereinstep (b) comprises adding the solvent in an amount to produce a mixturecontaining from about 5% to about 25% solids by weight.
 41. The methodof claim 34 wherein the catalyst comprises a tin compound or a titanatecompound.
 42. The method of claim 41 wherein the tin compound comprisesa compound selected from the group consisting of: (a) monoalkyltin(IV)hydroxide oxide, (b) monoalkyltin(IV) chloride dihydroxide, (c)dialkyltin(IV) oxide, (d) bistrialkyltin(IV) oxide, (e) monoalkyltin(IV)trisalkoxide, (f) dialkyltin(M) dialkoxide, (g) trialkyltin(IV)alkoxide, (h) a tin compound having the formula:

and (i) a tin compound having the formula:

wherein: R₂ is a C₁₋₄ primary alkyl group, and R₃ is C₁₋₁₀ alkyl group.43. The method of claim 41 wherein the titanate compound comprises acompound selected from the group consisting of: (a) tetraisopropyltitanate, (b) isopropyl titanate, (c) tetraalkyl titanate, (d) titanatetetraalkoxide, (e) a titanate compound having the formula:

wherein: each R is independently an alkyl group, or the two R₄ groupstaken together form a divalent aliphatic hydrocarbon group; R₅ is aC₂₋₁₀ divalent or trivalent aliphatic hydrocarbon group; R₆ is amethylene or ethylene group; and n is 0 or 1, (f) a titanate estercompound having at least one moiety of the formula:

wherein: each R₇ is independently a C₂₋₃ alkylene group; Z is O or N; R₈is a C₁₋₆ alkyl group or unsubstituted or substituted phenyl group;provided when Z is O, m=n=0, and when Z is N, m=0 or 1 and m+n=1, and(g) a titanate ester compound having at least one moiety of the formula:

wherein: each R₉ is independently a C₂₋₆ alkylene group; and q is 0or
 1. 44. A method for preparing a macrocyclic oligoester comprising thesteps of: (a) contacting a first compound having a structural formula:HO—R—OH   (I) wherein R is an alkylene, a cycloalkylene, or a mono- or apolyoxyalkylene group; with a second compound having a structuralformula: BOOC—A—COOB   (II) wherein A is a divalent aromatic group or analicyclic group, and B is hydrogen or an alkyl group; in the presence ofa catalyst comprising a titanate compound at a temperature between about140° C. and about 200° C. to produce a composition comprising ahydroxyalkyl-terminated polyester oligomer; (b) heating the compositioncomprising the hydroxyalkyl-terminated polyester oligomer at atemperature between about 180° C. and about 275° C. and at a pressurebetween about 5 torr and about 625 torr to produce a compositioncomprising an intermediate molecular weight polyester, wherein themolecular weight of the intermediate molecular weight polyester isbetween about 20,000 Daltons and about 70,000 Daltons; (c) heating thecomposition comprising the intermediate molecular weight polyester at atemperature between about 150° C. and about 200° C. in the presence of asolvent to produce a composition comprising a macrocyclic oligoester anda diol, wherein the solvent is capable of forming an azeotrope with thediol; and (d) separating the macrocyclic oligoester from the compositioncomprising the macrocyclic oligoester.